Catalytic NO removal reactions were investigated using a series of Mo carbides. Mo carbides were synthesized using Mo oxide (MoO₃ and methane gas (CH₄) at different heating rates and space velocities. Various characterization techniques, such as BET surface area and oxygen uptake measurements, were employed to characterize the different Mo carbides synthesized in this study. Depending on the preparative conditions, the BET surface areas ranged from 1 to 28 m²/g and the oxygen uptake values varied from 0.46 to 5.41 μmol/g. The Mo carbides were found to be active for NO removal reactions. Although the reactivity of some Mo carbide catalysts was exceeded by Pt/Al₂O₃ as catalyst, the steady state reaction activities of other Mo carbide catalysts were comparable to, or even higher than, that of the Pt/Al₂O₃ catalyst. These results imply that Mo carbides could be one of the more promising catalysts that might be able to replace platinum-group noble metal catalysts in the NO removal reactions. Moreover, there was a near-linear relationship between the No conversion and the particle size of the Mo carbides, suggesting the presence of the concept of structure-sensitivity for Mo carbides prepared in this study.